Virtual Synchronous Machine Current Limitation via Adaptive Admittance

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Solution Overview

Problem

Conventional methods for emulating synchronous machines using converters fail to handle network faults effectively, leading to excessive current amplitudes that exceed converter hardware constraints.

Innovation Solution

A control circuit for converters, employing a virtual admittance controller within an internal control loop, adjusts current amplitudes to emulate synchronous machine behavior, using a virtual admittance defined as Ys(S) = 1/Zvirt(S) = 1/Rvirt + s*Lvirt, allowing for dynamic and static emulation of synchronous machines, with adjustable ohmic and inductive parts to manage network and hardware constraints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional synchronous machine emulation methods are used, then the converter can emulate synchronous machine behavior under normal conditions, but excessive current amplitudes occur during network faults that exceed converter hardware constraints

Engineering Contradiction:

Improvesynchronous machine emulation reliabilityVSAvoidexcessive current amplitudes during network faults

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the virtual impedance parameters (resistance and inductance) based on the operating condition. During normal operation, the virtual impedance is set to emulate synchronous machine characteristics. During network faults, the virtual impedance parameters are modified to limit current amplitudes while maintaining the emulation function, thus resolving the contradiction between reliable emulation and fault current limitation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements dynamics by making the virtual impedance adaptive rather than fixed. The control system continuously monitors the operating state and dynamically adjusts the virtual impedance parameters to match the required emulation characteristics under normal conditions while providing current limitation during faults. This dynamic adaptation allows the system to maintain synchronous machine emulation reliability while preventing excessive current amplitudes during network faults.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If the converter is overdimensioned to handle fault currents, then network fault currents can be managed, but the converter size and cost increase

Engineering Contradiction:

Improvenetwork fault current handling capabilityVSAvoidconverter size and dimensioning

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent introduces virtual impedance as an intermediary element between the converter and the electrical network. This virtual impedance acts as a mediator that limits the fault currents before they reach the converter, allowing the converter to operate within its rated current capacity even during network faults. This approach eliminates the need to overdimension the converter while maintaining the ability to handle fault conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the mechanical approach of physically overdimensioning the converter with a control-based approach using virtual impedance. Instead of increasing the physical size and power rating of the converter hardware, the system uses electronic control to create a virtual impedance that limits fault currents, thereby substituting a mechanical solution with a more efficient electronic control solution.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If virtual impedance is used to limit currents, then converter hardware constraints are respected, but the emulation accuracy may be affected

Engineering Contradiction:

Improveconverter current constraintsVSAvoidsynchronous machine emulation accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent applies dynamics by making the virtual impedance adaptive rather than fixed. The control system continuously monitors the operating state and dynamically adjusts the virtual impedance parameters to match the required emulation characteristics under normal conditions while providing current limitation during faults. This dynamic adaptation allows the system to maintain synchronous machine emulation reliability while preventing excessive current amplitudes during network faults.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11774994B2Method for current limitation of a virtual synchronous machine

Publication Date: 2023.10.03 WOBBEN PROPERTIES GMBH

AI summary

Provided is a control module of a converter, in particular a power converter of a wind power installation, which is configured to control the converter in such a way that the converter emulates a behavior of a synchronous machine, comprising an, in particular internal, control loop which has an, in particular adjustable, virtual admittance by means of which the converter is controlled in order to emulate the behavior of the synchronous machine.